Aside from its externals, the only way to determine the quality of a watch is to look at the movement. The only way looking at a movement will matter is if you learn to tell the difference between the common chinese movements used in reps and the gen ETA movements and their copies. There is plenty of info on this site to learn these things. Many of the sellers may not even let you open the watch up at all. One thing's for sure: don't believe anything they say. Confirm everything yourself, especially if they're trying to charge you top dollar for a "swiss" version. BTW there's no such thing as a swiss replica, just asian reps with swiss movements.
When I went to Thailand last year, every vendor "guaranteed" that their watches were 100% perfect replicas while handing me garbage such as quartz watches stamped as automatics and non-working chronos with crooked logos and missing hands. Even when I asked for the good stuff, I never found anything close to approaching the UPO, Link and SFSO qualities that we're used to. Funny thing is, many provided actual catalogs to prove how good their wares were. They only helped me see all the mistakes. Most of the vendors on the street are just pushing $10-$20 junk for casual tourists who get excited at the first rollie they see. I know the good stuff's out there, but they seem to be the exception by far rather than the norm. Unfortunately I didn't get to go to Maria's stall.
I don't know how GZ will compare, but even though I had been pretty excited about the watch markets in Thailand, the conclusion I brought home was that it's better to just get your fix from the recommended dealers here. That's the only way to know what you're getting, plus you'll have some recourse if you get a lemon (which you will eventually).